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Managing Algae in Greenhouses by Paul Pilon

November 09, 2010

Algae are a diverse grouping of plants that commonly appears in greenhouses and can be very problematic for some growers. They are simple plants that primarily reproduce vegetatively by single cell division or fragmentation of colonies; they also have a sexual cycle that produces zoospores.

Algae growth commonly occurs on floors, walkways, walls, water pipes, equipment, on the surface of the growing media, and can clog irrigation and misting lines. Algae often form an impermeable layer on the media surface which prevents water from entering the root zone. It often causes walkways to become slippery, posing a liability risk for employees and customers. Additionally, algae provide a breeding habitat for fungus gnats and a food source for shore flies.

Initially, algae are introduced into greenhouses from the peat moss used in growing mixes and through irrigation supplies. Once inside the greenhouse’s moist environment and provided nutrients through the fertilizers growers use, it begins to grow and quickly flourishes.

Algae can be difficult to control since it thrives under the same growing conditions as greenhouse crops do: adequate light, moisture, and nutrients. In most cases, growers need to use a combination of strategies including various cultural, sanitation, and chemical methods. Several of these control methods are listed below.

Cultural

  • Reduce excessive moisture from improper irrigation and misting practices.
  • Avoid over-watering slow growing plants and crops early in the production cycle.
  • Allow the surface of the growing mix to dry our between irrigations.
  • Reduce excessive nutrients delivered to crops. Do not provide ‘luxury’ fertility levels - feed using the appropriate nutrients and application intervals.
  • Use horizontal air flow fans to reduce moisture and condensation in the greenhouse.

Sanitation

  • Avoid excessive leaching of nutrients as this may lead to algae growth under benches.
  • Prevent puddles on the floors by fixing any irrigation leaks and providing the proper drainage.
  • Eliminate any drips from the ceiling caused by condensation.
  • Keep the production site free of plant debris, spilled potting substrates, and weeds.
  • Use weed mat barriers over sand and gravel floors to reduce both weed and algae growth.
  • Avoid using clear or translucent hoses and distribution pipes - use black tubing for irrigation lines.
  • Avoid using surface water which is high in nutrients and may contribute to algae growth. Control the algae in these sources (ponds) before irrigating crops using filters, chlorine, chlorine dioxide, copper ionization, hydrogen dioxide, or ozone.

Algaecides

  • Use algaecides to clean the production site between crops or non-crop areas during production using quaternary ammonium compounds, hydrogen dioxides, or sodium carbonate peroxyhydrates.
  • Hydrogen dioxides are often labeled for applications to crop areas.

The key to managing algae is to prevent it from becoming established using a variety of control strategies.  Algae management should begin before a crop is started and continue throughout the entire production cycle.

Paul Pilon
Perennial Solutions Consulting
paul@perennialsolutions.com

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